This invention relates to a high pressure electric discharge lamp, and more particularly to such a lamp provided with means for securing the supporting part of the electrode rods thereof in the direction of the longitudinal axis of the lamp.
Parts supporting the electrode rod of a high-pressure electric discharge lamp have proved necessary since the seal extending only over a relatively short piece of the rod-shaped electrode lead-in wire is often exposed to a heavy strain caused by the weight and the length of the electrode rod. This may cause cracks in the sealing material so that the seal becomes leaky at the electrode lead-in wire.
It is known to use a supporting part which is provided in the envelope neck between the electrode and the electrode seal or the vacuum-tight passage of the lead-in wire, respectively, for instance, a cylindrical ring having a coefficient of expansion similar to that of the envelope material (shown in DE-PS No. 1 132 242). The surface area of the ring is sealed to the envelope neck by the cylindrical ring. From DE-OS No. 26 23 099 there is known a supporting part which is not sealed to the envelope neck. Various possibilities of securing the supporting part are indicated which require a precise adjustment and with which the finished lamp is disadvantageously treated at certain regions with temperatures up to the softening point of the envelope material.
In contrast, it is the object of the present invention to provide a lamp having parts which support the rod-shaped electrode, and whose manufacture is simpler and safer.